Concurrent touch and negative pixel scan

ABSTRACT

A concurrent touch and negative pixel scan performed at a touch panel is disclosed. The concurrent scan can include sensing an object proximate to the touch panel and sensing a negative pixel effect, based the object&#39;s grounding condition, at the touch panel, at the same time. As a result, sense signals indicative of the proximity of the object and coupling signals indicative of the negative pixel effect&#39;s magnitude can be captured concurrently. Because the negative pixel effect can cause errors or distortions in the sense signals, the coupling signals can be used to compensate the sense signals for the negative pixel effect.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/234,0954, filed Sep. 15, 2011 and published on Mar. 21, 2013 as U.S.Publication No. 2013-0069905, the entire disclosure of which isincorporated herein by reference in its entirety for all purposes.

FIELD

This relates generally to touch panels and more particularly toconcurrent scans of touch panels.

BACKGROUND

Many types of input devices are presently available for performingoperations in a computing system, such as buttons or keys, mice,trackballs, joysticks, touch sensor panels, touch screens and the like.Touch sensitive devices in particular are popular because of their easeand versatility of operation as well as their declining price. A touchsensitive device can include a touch sensor panel, which can be a clearpanel with a touch sensitive surface. In some instances, a touchsensitive device can also include a display device such as a liquidcrystal display (LCD) that can be positioned partially or fully behindthe panel or integrated with the panel so that the touch sensitivesurface can cover at least a portion of the viewable area of the displaydevice. The touch sensitive device can allow a user to perform variousfunctions by touching or hovering over the touch sensor panel using afinger, stylus or other object at a location on the panel. In theinstance of the display device, the touching or hovering location canoften be dictated by a user interface (UI) being displayed by thedisplay device. In general, the touch sensitive device can recognize atouch or hover event and the position of the event on the touch sensorpanel. The computing system can then interpret the event and thereaftercan perform one or more functions based thereon.

When the object touching or hovering over the touch sensor panel ispoorly grounded, data outputs indicative of the touch or hover event canbe erroneous or otherwise distorted. The possibility of such erroneousand distorted outputs can further increase when two or more simultaneoustouch or hover events occur at the touch sensor panel.

Many touch sensitive devices are now recognizing simultaneous touch orhover events, in addition to single touch or hover events, as additionalinputs to allow the user to perform various functions associated withthe simultaneous events. As such, techniques to address poorly groundedobjects that cause the simultaneous events are becoming quite important.The challenge is to develop a technique that appropriately addresses theerroneous of distorted outputs, yet does so in an efficient, effectivemanner.

SUMMARY

This relates to a concurrent touch and negative pixel scan performed ata touch panel of a touch sensitive device. The concurrent scan caninclude sensing an object proximate to the touch panel and sensing anegative pixel effect, based the object's grounding condition, on thetouch panel, at the same time. As a result, sense signals indicative ofthe proximity of the object and coupling signals indicative of thenegative pixel effect's magnitude can be captured concurrently. Thenegative pixel effect can cause errors or distortions in the sensesignals, particularly when the sense signals indicate the proximateobject touching or hovering over multiple touch panel locations.Accordingly, the coupling signals can be applied to the sense signals tocompensate the sense signals for the negative pixel effect. In oneexample, a single concurrent scan can be performed at the touch panelduring a scan period. In another example, multiple successive concurrentscans can be performed at the touch panel during a scan period. Byperforming the touch and negative pixel scan concurrently, rather thansequentially, the touch sensitive device can advantageously saveprocessing time and power consumption, while improving touch and hoversensing, particularly for multiple simultaneous touch or hover events.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary touch panel that can have a concurrenttouch and negative pixel scan according to various embodiments.

FIG. 2 illustrates an exemplary touch sensitive device that can performa concurrent touch and negative pixel scan at a touch panel according tovarious embodiments.

FIGS. 3A, 3B, and 3C illustrate an exemplary touch sensitive device thatcan switch touch panel configuration for a concurrent touch and negativepixel scan according to various embodiments.

FIG. 4 illustrates an exemplary touch sensitive device that can performnoise rejection during a concurrent touch and negative pixel scan at atouch panel according to various embodiments.

FIG. 5 illustrates an exemplary method for performing a concurrent touchand negative pixel scan at a touch panel according to variousembodiments.

FIG. 6 illustrates another exemplary method for performing a concurrenttouch and negative pixel scan at a touch panel according to variousembodiments.

FIG. 7 illustrates an exemplary method for performing a concurrent touchand negative pixel scan at a touch panel and for rejecting noise in thepanel according to various embodiments.

FIG. 8 illustrates an exemplary computing system that can perform aconcurrent touch and negative pixel scan at the system's touch panelaccording to various embodiments.

FIG. 9 illustrates an exemplary mobile telephone that can perform aconcurrent touch and negative pixel scan at the telephone's touch panelaccording to various embodiments.

FIG. 10 illustrates an exemplary digital media player that can perform aconcurrent touch and negative pixel scan at the player's touch panelaccording to various embodiments.

FIG. 11 illustrates an exemplary portable computer that can perform aconcurrent touch and negative pixel scan at the computer's touch panelaccording to various embodiments.

DETAILED DESCRIPTION

In the following description of example embodiments, reference is madeto the accompanying drawings in which it is shown by way of illustrationspecific embodiments that can be practiced. It is to be understood thatother embodiments can be used and structural changes can be made withoutdeparting from the scope of the various embodiments.

This relates to a concurrent touch and negative pixel scan performed ata touch panel of a touch sensitive device. The concurrent scan caninclude sensing an object proximate to the touch panel, i.e., the“touch” scan, and sensing a negative pixel effect, based the object'sgrounding condition, at the touch panel, i.e., the “negative pixel”scan, at the same time. As a result, sense signals indicative of theproximity of the object and coupling signals indicative of the negativepixel effect's magnitude can be captured concurrently. Because thenegative pixel effect can cause errors or distortions in the sensesignals, particularly when the sense signals indicate the proximateobject touching or hovering over multiple touch panel locations, thecoupling signals can be applied to the sense signals to compensate thesense signals for the negative pixel effect.

In some embodiments, a single concurrent scan can be performed at thetouch panel during a scan period. In alternate embodiments, multiplesuccessive concurrent scans can be performed at the touch panel during ascan period, where each scan can be performed with a different touchpanel configuration.

In some embodiments, noise can be introduced into the touch panel byadjacent circuitry. Accordingly, the concurrent scan can further includesensing the introduced noise. The introduced noise can then be rejectedfrom the touch panel while the sense signals and coupling signals arebeing processed.

Some present techniques perform the touch scan and the negative pixelscan separately, in sequence, either during a scan period or duringsuccessive scan periods. By performing the touch and negative pixel scanconcurrently, according to various embodiments, the touch sensitivedevice can advantageously save processing time and power consumption,while improving touch and hover sensing, especially for multiplesimultaneous touch or hover events.

FIG. 1 illustrates an exemplary touch panel that can have a concurrenttouch and negative pixel scan according to various embodiments. In theexample of FIG. 1, touch sensor panel 124 can include an array of pixels126 that can be formed at the crossings of rows of drive lines 101(D0-D3) and columns of sense lines 102 (S0-S3). The drive lines 101 canbe used to drive the panel 124 with stimulation signals Vstim 116. Thesense lines 102 can be used to transmit sense signals, in response tothe stimulation signals 116, indicative of a touch or hover at the panel124. Each pixel 126 can have an associated mutual capacitance Csig whenthe drive line 101 forming the pixel is stimulated with a stimulationsignal 116.

When an object, e.g., a finger, touches or hovers over the panel 124 atthe location of the stimulated pixel 126, the capacitance Csig canreduce by ΔCsig due to charge being shunted from the stimulated pixelthrough the touching or hovering object to ground. The reduced Csig canbe transmitted by the associated sense lines 102 and captured during apanel scan for processing by sense circuitry (not shown). In thisexample, drive line D0 can be stimulated with the stimulation signal116, forming a mutual capacitance Csig between the stimulated drive lineD0 and the crossing sense lines S0-S3. When an object touches or hoversover the panel 124 at stimulated pixel 126-a formed by drive line D0 andsense line S1, the mutual capacitance Csig at pixel 126-a can be reducedby ΔCsig.

In some embodiments, multiple drive lines 101 can be concurrentlystimulated with stimulation signals 116 to detect multiple objects,e.g., multiple fingers, touching or hovering over the panel 124. If theobjects are properly grounded, multiple reduced Csig signals can betransmitted by the associated sense lines 202 and captured during apanel scan for processing by the sense circuitry.

However, if the objects are not properly grounded, they can capacitivelycouple with the panel 124, sending some of the charge from thestimulated pixels 126 back into the panel. As a result, instead of thecapacitance Csig being reduced by ΔCsig at the pixels 126 where thetouch or hover occurs, Csig can only be reduced by (ΔCsig−Cneg), whereCneg can represent a so-called “negative capacitance.” Accordingly, theCsig signals captured during the scan can be attenuated. In thisexample, drive lines D0, D2 can be stimulated with stimulation signals116, forming a mutual capacitance Csig between the stimulated drive lineD0 and the crossing sense lines S0-S3 and between the stimulation driveline D2 and the crossing sense lines S0-S3. When poorly grounded objectstouch or hover over the panel 124 at stimulated pixels 126-a and 126-cformed by drive line D0 and sense line S1 and by drive line D2 and senseline S2, respectively, the mutual capacitance Csig at pixels 126-a and126-c can only be reduced by (ΔCsig−Cneg), thereby attenuating the sensesignals transmitted on sense lines S1, S2 and captured during the panelscan.

Not only can the pixels 126-a and 126-c where the touch or hover occursbe affected, but adjacent pixels 126-b and 126-d that are not beingtouched or hovered over can also be affected. Rather than experience nochange in capacitance Csig, the adjacent pixels 126-b and 126-d can givethe appearance of a so-called “negative pixel” or a theoretical negativeamount of touch, i.e., an increase in Csig. This can be because thepoorly grounded object can couple some of the charge from the stimulatedpixel 126-a and 126-c back into the panel 124, which can cause anapparent increase in charge at pixel 126-b and an apparent increase incharge at pixel 126-d when the sense lines are scanned for touchactivity. Accordingly, the Csig signals for the adjacent pixels 126-band 126-d can have “negative pixel” values captured during the scan.

When the drive lines 101 are stimulated, they can capacitivelycross-couple with other drive lines through the touching or hoveringobjects. In this example, stimulated drive line D0 can capacitivelycross-couple (illustrated by Cdd) with drive line D1 through thetouching or hovering objects, and with other drive lines D2, D3 as well.For example, as the objects touch or hover over the panel 124 atstimulated pixels 126-a and 126-c, cross-coupling between thecorresponding drive lines D0 and D2 can increase. Because of thenegative pixel effect, the cross capacitance Cdd can be stronger than itwould have been otherwise. The cross capacitance Cdd signals on thedrive lines can be captured during a panel scan for processing by thesense circuitry.

Accordingly, during a panel scan, two capacitance measurements can becaptured—cross capacitance Cdd, indicative of the negative pixel effect,and mutual capacitance Csig adjusted either by a proper touch or hoveror by the negative pixel effect, indicative of a touch or hover at thepanel—in essence, performing a touch scan and a negative pixel scanconcurrently. The cross capacitance Cdd can be used to determine thenegative pixel effect and to compensate the mutual capacitance Csigtherefor. Various embodiments described below can measure Cdd andchanges in Csig, determine the negative pixel effect from Cdd, andcompensate Csig therefor.

Although various embodiments can be described and illustrated herein interms of multi-touch, mutual capacitance touch panels, it should beunderstood that the various embodiments are not so limited, but can beadditionally applicable to self capacitance panels and single stimulustouch panels. It should be further understood that the variousembodiments are not limited to the drive and sense line configurationdescribed and illustrated herein, but can include other configurationsaccording to the needs of the touch panel.

FIG. 2 illustrates an exemplary touch sensitive device that can performa concurrent touch and negative pixel scan of a touch panel according tovarious embodiments. In the example of FIG. 2, touch sensitive device200 can include touch panel 224, drive circuitry, and sense circuitry.The drive circuitry can include touch buffers 220 coupled to drive lines201 of the touch panel 224 to transmit stimulation signals Vstim to thepanel to drive the panel. Vstim can be either a positive (+) phasestimulation signal Vstim+ or a negative (−) phase stimulation signalVstim− having the same waveform as Vstim+ inverted about a commonvoltage. Each buffer 220 can transmit either Vstim+ or Vstim− based onthe drive pattern of the device 200. In some embodiments, the drivepattern can be defined by a stimulus matrix M, which can include data togenerate the stimulation signals, such as the phases of the stimulationsignals for each drive line, which drive lines are stimulatedconcurrently, and so on. During a panel scan, scan logic (not shown) canuse the stimulus matrix M data to control the drive pattern.

As stated previously, the drive lines 201 can capacitively cross-couple(illustrated by Cdd) with each other, either through the panel 224 orthrough objects touching or hovering over the drive lines. Asillustrated in FIG. 2, the cross-coupling between two drive lines 201can induce a voltage Vdd at the output of each touch buffer 220 of thecoupled drive lines. As a result, each buffer 220 can output a compositesignal that includes a stimulation signal Vstim and a drive couplingsignal Vdd to drive the touch panel 224. Each buffer 220 can include aresistor Rfb_tx in a feedback loop of the buffer to sense the Vdd signalin preparation for negative pixel compensation based on the Vdd signal.The voltage drop across the resistor Rfb_tx, amounting to the Vddsignal, can be a function of the cross-coupling capacitance Cdd and canbe defined as follows.

Vdd(n,m,s,t)=ω_(STM)·Rfb_tx(n)·Cdd(n,m)·Vstim·[M(n,s)−M(m,s)]·cos(ω_(STM) ·t),   (1)

where Vdd(n,m,s,t)=voltage across Rfb_tx(n) due to coupling betweentouch buffer n and touch buffer m for panel scan step s,ω_(STM)=stimulus frequency in radians, Rfb_tx(n)=feedback resistance oftouch buffers n and m, Cdd(n,m)=coupling between touch buffers n and m,Vstim=amplitude of sinusoidal stimulation signal, M(n,s)=touch scanstimulus matrix M coefficient for touch buffer n and panel scan step s,and M(m,s)=touch scan stimulus matrix M coefficient for touch buffer mand panel scan step s. For a given touch buffer, a total of r·(r−1)coupling terms can be resolved, where r=total number of touch buffers.

To isolate the sensed Vdd signal, the drive circuitry can includemultiplexers 222, differential anti-aliasing filter (AAF) 236, anddifferential analog-to-digital converter (ADC) 238. Multiplexer 222-acan receive the downstream resistor Vdd signals Vddo of the coupledbuffers 220. Similarly, multiplexer 222-b can receive the upstreamresistor Vdd signals Vddi of the coupled buffers 220. The multiplexers222 can select one of the Vddo and Vddi signals based on selectionsignal SEL and can input the selected signals to the AAF 236 and the ADC238. The ADC 238 can then output a digital signal proportional to thevoltage drop across the resistor, i.e., the Vdd signal, in preparationfor negative pixel compensation based on the Vdd signal. In theseembodiments, the multiplexers 222 can allow sharing of the AAF 236 andADC 238 between multiple touch buffers 220. In alternate embodiments,the multiplexers 222 can be omitted and each touch buffer 220 can haveits own AAF 236 and ADC 238.

The sense circuitry can include sense amplifiers 234 coupled to senselines 202 of the touch panel 224 to receive sense signals indicative ofa change in Csig and a sensed touch or hover at the panel. In someembodiments, each sense line 202 can connect to a different senseamplifier 234. In some embodiments, multiple sense lines 202 can share asense amplifier 234, with a switch between the sense lines and the senseamplifier to sequentially connect each sense line to the amplifier.During a panel scan, scan logic (not shown) can control the sensecircuitry for capturing and processing the sense signals.

The sense circuitry can also include AAF 246, ADC 248, digitaldemodulator 242, and vector operator 244 to process the sense signals.The AAF 246 can receive a sense signal from a sense amplifier 234 andlow-pass filter the received signal. The ADC 248 can receive thefiltered signal from the AAF 246 and convert the filtered signal to adigital signal. The digital demodulator 242 can receive a digital sensesignal from the ADC 248 and use programmable delay 242-a to phase shiftthe sense signal so as to align the signal with a demodulation signalgenerated by a receive NCO (not shown) in order to maximize thedemodulation gain, mixer 242-b to multiply the phase-shifted sensesignal with the demodulation signal so as to demodulate the sensesignal, and integrator 242-c to integrate the demodulated sense signal.The vector operator 244 can receive an integrated sense signal from thedemodulator 242 and output touch panel pixel capacitances Cds,indicative of the coupling between drive and sense lines, using mixer244-a to multiply the integrated signal with a decode matrix M′ todecode the signal and using integrator 244-b to integrate the decodedsense signal, thereby obtaining the pixel capacitances. In someembodiments, the decode matrix M′ can be the inverse of the stimulusmatrix M. The decode matrix M′ can include data for decoding theintegrated sense signal. As described previously, the drive linecross-coupling can induce a Vdd signal into the panel 224. As a result,the outputted capacitances Cds from the vector operator 244 can includethe cross-coupling capacitances Cdd and, hence, the negative pixeleffect to be compensated for.

The digital demodulator 242 and the vector operator 244 can also be usedto process the Vdd signals to output the cross-coupling capacitancesCdd, indicative of the negative pixel effect. The demodulator 242 canreceive a Vdd signal from the differential ADC 238 and use theprogrammable delay 242-a, the mixer 242-b, and the integrator 242-c toprocess the Vdd signal, in the same manner as described previouslyregarding the sense signal. The vector operator 244 can receive anintegrated Vdd signal from the demodulator 242 and, using across-coupling matrix N at the mixer 224-a, output drive linecross-coupling capacitances Cdd. In some embodiments, the cross-couplingmatrix N can be the inverse of the stimulus matrix M. In otherembodiments, the cross-coupling matrix N can be slightly different fromthe inverse of the stimulus matrix M, where the cross-coupling matrix Ncan include some data modifications, e.g., based on the stimulationsignal Vstim phases between the cross-coupled drive lines. Thecross-coupling matrix N can include data for decoding the integrated Vddsignal. During a panel scan, scan logic (not shown) can control thesense circuitry for capturing and processing the cross-coupling signals.An example multi-stimulus demodulation process is described in U.S.Patent Application No. 2010-0060593, “Phase Compensation forMulti-Stimulus Controller.”

A processor (not shown) can receive the pixel capacitances Cds,indicative of the touch or hover sensing and including some indicationof the drive line cross-coupling as well, and the drive linecross-coupling capacitances Cdd, indicative of the drive linecross-coupling. The processor can then apply the Cdd capacitances to theCds capacitances, thereby compensating the touch and hover sensing forthe negative pixel effect. An example negative pixel compensationprocess is described in U.S. Patent Application No. 2011-0006832,“Negative Pixel Compensation.”

In an example panel scan of the touch sensitive device 200 of FIG. 2,stimulation signal Vstim+ can drive a drive line of the touch panel 224and stimulation signal Vstim− can drive another drive line of the panelaccording to a drive pattern (based on stimulus matrix M) of the touchpanel 224. As a poorly grounded object touches or hovers over the panelat pixel locations corresponding to the stimulated drive lines, theobject can undesirably capacitively couple with the touch panel 224,thereby introducing charge back into the panel that shows up on thedrive lines. In particular, the introduced charge can increase across-coupling between the drives lines, that shows up as cross-couplingsignal Vdd. The Vstim+Vdd signals can drive the touch panel 224 togenerate one group of sense signals, indicative of the touching orhovering object, that are attenuated by a negative capacitance, andanother group of sense signals, at pixel locations where the object isnot touching or hovering, that have negative pixel values, all due tothe object's poor grounding. The sense signals and the cross-couplingsignals can be captured and processed using the drive and sensecircuitry, described above. Effectively, this can be a sense signal (ortouch) scan and a cross-coupling signal (or negative pixel) scanperformed concurrently.

It should be understood that the touch sensitive device is not limitedto that shown in FIG. 2, but can include additional and/or othercomponents for performing a concurrent touch and negative pixel scanaccording to various embodiments. It should further be understood thatadditional drive lines and associated drive circuitry and sense linesand associated sense circuitry can perform in the same manner as thoseillustrated in FIG. 2.

FIG. 2 illustrates one drive-sense line configuration, where the drivelines can drive the touch panel 224 and capacitively cross-couple, whilethe sense lines transmit sense signals from the panel. In an alternatedrive-sense line configuration, the sense lines can act as drive linesto drive the touch panel and capacitively cross-couple, while the drivelines act as sense lines to transmit sense signals from the panel. FIG.3A illustrates switching circuitry that allows a touch sensitive deviceto switch between the two configurations. In some embodiments, the touchsensitive device can switch to a single configuration and perform thetouch and negative pixel scan in that configuration, using that captureddata for negative pixel compensation. In alternate embodiments, thetouch sensitive device can switch between the two configurations andperform the touch and negative pixel scan in both configurations, usingboth sets of captured data for negative pixel compensation. The multiplescans can be performed during the same scan period or during differentsuccessive scan periods, based on the needs of the touch panel.

In the example of FIG. 3A, touch sensitive device 300 can be the same astouch sensitive device 200 of FIG. 2, except for the addition ofmultiplexers 322, 326. Multiplexer 322 can receive the output of touchbuffer 220 and select, based on selection signal LSEL, whether to couplethe output to drive line 301 or sense line 302 to drive the touch panel224 and to sense line cross-coupling. Multiplexer 326 can output tosense amplifier 234 and select based on the selection signal LSELwhether to couple the drive line 301 or the sense line 302 to theamplifier in order to transmit sense signals from the touch panel 224 tothe amplifier. For example, LSEL can select the drive lines 301 to drivethe touch panel 224 and to sense drive line cross-coupling and the senselines 302 to transmit sense signals from the panel (illustrated by LSELlogic 1). Conversely, LSEL can select the sense lines 302 to drive thetouch panel 224 and to sense line cross-coupling and the drive lines 301to transmit sense signals from the panel (illustrated by LSEL logic 0).Using these configurations, both drive line cross-coupling capacitancesCdd and sense line cross-coupling capacitances Css can be sensed andused to compensate for negative pixel effect.

When the sense lines 302 act as drive lines, either the same stimulusmatrix M, decode matrix M′, and/or cross-coupling matrix N, as for thedrive lines, can be used or a different stimulus matrix M″, decodematrix M′″, and/or cross-coupling matrix N′ can be used, based on thedrive and sense line characteristics.

FIG. 3B illustrates exemplary components of drive line cross-couplingcapacitance (illustrated by Cdd in FIG. 3A) when the drive lines 301drive the touch panel 224 and an object, e.g., a finger, touches thepanel. In the example of FIG. 3B, as a finger touches or hovers over thetouch panel 224, several capacitances can form to make up thecross-coupling capacitance Cdd between stimulated drive lines 301, whichcan be defined as follows.

Cdd=C _(dd) _(_) _(neg) _(_) _(pix) +C _(dd) _(_) _(mut) +ΔC _(dd) _(_)_(mut),   (2)

where the cross-coupling capacitance due to the negative pixel effectC_(dd) _(_) _(neg) _(_) _(pix) can be defined as

$\begin{matrix}{{C_{{dd\_ neg}{\_ pix}} = \frac{C_{{fD}\; 0} + C_{{fD}\; 1}}{C_{gnd} + C_{ftot}}},} & (3)\end{matrix}$

where C_(fD0)=the coupling capacitance between the finger and drive lineD0, C_(fD1)=the coupling capacitance between the finger and drive lineD1, C_(dd) _(_) _(mut)=the coupling capacitance between the drive linesD0, D1, ΔC_(dd) _(_) _(mut)=the variation in C_(dd) _(_) _(mut) due tothe presence of the finger, C_(gnd)=C_(body-earth)+C_(earth-chassis)(the sum of the capacitance between the object's, e.g., user's, body andthe earth and the capacitance between the earth and the chassis of thedevice housing the touch panel), and C_(ftot)=the coupling capacitanceof the finger to all the drive lines and sense lines.

FIG. 3C similarly illustrates exemplary components of sense linecross-coupling capacitance (illustrated by Css in FIG. 3A) when thesense lines 302 drive the touch panel 224 and an object, e.g., a finger,touches the panel. In the example of FIG. 3C, as a finger touches orhovers over the touch panel 224, several capacitances can form to makeup the cross-coupling capacitance Css between stimulated sense lines302, which can be defined as follows.

Css=C _(ss) _(_) _(neg) _(_) _(pix) +C _(ss) _(_) _(mut) +ΔC _(ss) _(_)_(mut),   (4)

where the cross-coupling capacitance due to the negative pixel effectC_(ss) _(_) _(neg) _(_) _(pix) can be defined as

$\begin{matrix}{{C_{{{ss}{\_ neg}}{\_ pix}} = \frac{C_{{fS}\; 0} + C_{{fS}\; 1}}{C_{gnd} + C_{ftot}}},} & (5)\end{matrix}$

where C_(fS0)=the coupling capacitance between the finger and sense lineS0, C_(fS1)=the coupling capacitance between the finger and sense lineS1, C_(ss) _(_) _(mut)=the coupling capacitance between the sense linesS0, S1, ΔC_(ss) _(_) _(mut)=the variation in C_(ss) _(_) _(mut) due tothe presence of the finger, C_(gnd)=C_(body-earth)+C_(earth-chassis)(the sum of the capacitance between the object's, e.g., user's, body andthe earth and the capacitance between the earth and the chassis of thedevice housing the touch panel), and C_(ftot)=the coupling capacitanceof the finger to all the drive lines and sense lines.

In addition to negative pixel effects on touch and hover sensing of thetouch panel, noise introduced into the panel by adjacent circuitry canalso be problematic. For example, a display, e.g., a liquid crystaldisplay (LCD), adjacent to a touch panel in a touch sensitive display,can introduce noise into the panel when the LCD's Vcom layer undesirablycapacitively couples with the panel. Accordingly, noise rejectioncircuitry can be used to reject the noise coupled from the LCD to thetouch panel.

FIG. 4 illustrates exemplary noise rejection circuitry that can be usedto reject noise in a touch panel. In the example of FIG. 4, touchsensitive device 400 can be the same as touch sensitive device 200 ofFIG. 2, except for the addition of noise rejection circuitry and an LCD.LCD 430 via its Vcom layer (not shown) can capacitive couple(illustrated by Cp) to the panel 224 via the touch buffers 220. Asillustrated in FIG. 4, the voltage across the touch buffer resistorRfb_tx can have three components, a Vdd signal induced by thecross-coupling between drive lines, a Vcom signal induced by thecoupling between the LCD 430 and the touch panel 224, and a Vd signalcorresponding to a load capacitance Cd driven with a sinusoidalstimulation signal Vstim by the touch buffer 220. The Vd signal can bedefined as follows.

Vd(n,s,t)=ω_(STM) ·Rfb_tx·Cd·Vstim·M(n,s)·cos(ω_(STM) ·t),   (6)

where the Vd(n,s,t) signal across Rfb_tx can be caused by touch buffer ndriving load capacitance Cd at a phase according to stimulus matrix Mcoefficient M(n,s) for buffer n and panel scan step s at frequencyω_(STM) (in radians). The Vdd+Vcom+Vd signal can be sensed and isolatedthrough the multiplexers 222, AAF 236, and ADC 238, in a similar manneras described in FIG. 2 regarding the Vdd signal. The Vdd+Vcom+Vd signalcan be outputted from the ADC 238 and inputted to the noise rejectioncircuitry.

The noise rejection circuitry can include summer 452-b to receive theVdd+Vcom+Vd signals from the touch buffers 220. Across all the touchbuffers 220, the number of positive phases and negative phases for theVdd signals can be balanced because Vdd only occurs when the buffersthat drive their corresponding cross-coupling capacitances Cdd are inopposite phase. As such, at summer 452-b, the Vdd signals can canceleach other out, leaving the Vd and Vcom signals.

To cancel out the Vd signals, a compensation signal Vdc can be added tosummer 452-b to compensate for any imbalance between the number ofpositive phases and negative phases for the Vstim signals to the touchbuffers 220. This is because the Vd signals are generated as a result ofthe Vstim signals and hence carry the same phase as their correspondingVstim signals. For example, if there are 15 touch buffers and 9 aredriven with Vstim+ and 6 are driven with Vstim−, there can be animbalance of +3 (i.e., +9−6=+3) in the Vstim signals and hence in the Vdsignals inputted to the summer 452-b. Accordingly, the compensationsignal Vdc can be added to the summer 452-b to cancel the imbalance of+3. By doing so, the Vd signals can be canceled, leaving the Vcomsignal.

To generate the compensation signal Vdc at an optimum phase andamplitude, the noise rejection circuitry can include programmable delay458 to receive a Vstim signal from a transmit NCO (not shown) and tophase shift the Vstim signal to the optimum phase. The noise rejectioncircuitry can further include programmable scaler 456 to receive thephase-shifted Vstim signal and to adjust the amplitude of the signalusing a programmable scale factor. The scaler 456 can then output to thesummer 452-b the compensation signal Vdc at the optimum phase andamplitude to cancel out the Vd signals. The summer 452-b can then outputthe Vcom signal.

The noise rejection circuitry can include summers 452-a, 452-c toreceive the Vcom signal from the summer 452-b and to subtract out theVcom signal from the output of the ADC 238, i.e., the cross-couplingsignals, thereby rejecting the noise introduced by the LCD 430. Thenoise rejection circuitry can also include programmable scaler 454 toscale the Vcom signal inputted from summer 452-b, using a programmablescale factor, in order to subtract the scaled Vcom signal from the sensesignals. The noise rejection circuitry can include summer 452-d toreceived the scaled Vcom signal and to subtract the scaled Vcom signalfrom the sense signals, thereby rejecting the noise introduced by theLCD 430. The sense signals and the cross-coupling signals, with thenoise rejected therefrom, can then be used in a similar manner asdescribed previously to compensate the sense signals for negative pixeleffects.

It is to be understood that the noise rejection circuitry is not limitedto that of FIG. 4, but can include additional and/or other componentsand configurations according to various embodiments. It is further to beunderstood that noise is not limited to being introduced by an LCD, butcan be introduced by any other circuitry adjacent to a touch panel.

FIG. 5 illustrates an exemplary method for performing a concurrent touchand negative pixel scan at a touch panel according to variousembodiments. In the example of FIG. 5, a scan of the touch panel can beperformed to concurrently capture sense signals, indicative of atouching or hovering object at the panel, and cross-coupling signals,indicative of a negative pixel effect at the panel due to poor groundingof the object (505). During the scan, multiple stimulation signals candrive the panel along drive lines of the panel. The drive lines cancapacitively cross-couple with each other to produce cross-couplingcapacitances Cdd. The drive lines and sense lines of the panel can alsocapacitively couple to produce mutual capacitance Csig. As a poorlygrounded object touches or hovers over the panel at multiple locations,the object can cause a negative pixel effect in the panel, which can beobserved in the cross-coupling capacitances Cdd and the change in mutualcapacitance Csig. Concurrently, the sense signals can be captured,representative of the change in Csig and the negative pixel effect, andthe cross-coupling signals can be captured, representative of thenegative pixel effect (510). The captured sense signals andcross-coupling signals can be processed (520). In some embodiments, thesense signals can be processed using decode matrix M′ to obtain thepixel capacitances indicative of the touch or hover at the touch panel.Similarly, the cross-coupling signals can be processes usingcross-coupling matrix N to obtain cross-coupling capacitances indicativeof the negative pixel effect. The processed cross-coupling signals canbe applied to the processed sense signals to compensate the sensesignals for the negative pixel effect (525). In some embodiments, thecross-coupling signals can be subtracted from the sense signals toperform the compensation.

FIG. 6 illustrates another exemplary method for performing a concurrenttouch and negative pixel scan at a touch panel according to variousembodiments. In the example of FIG. 6, two scans can be performed, wherethe first scan is performed on the touch panel in a first drive-senseline configuration and the second scan is performed after switching thepanel to a second drive-sense line configuration. In the firstdrive-sense configuration, the drive lines can drive the panel andcapacitively cross-couple, while the sense lines transmit the sensesignals for processing. This first scan can be the same as thatdescribed in FIG. 5. That is, a scan of the touch panel can be performedto concurrently capture sense signals, indicative of a touching orhovering object at the panel, and cross-coupling signals, indicative ofa negative pixel effect at the panel due to poor grounding of the object(605). During the scan, multiple stimulation signals can drive the panelalong drive lines of the panel. The drive lines can capacitivelycross-couple with each other to produce cross-coupling capacitances Cdd.The drive lines and sense lines of the panel can also capacitivelycouple to produce mutual capacitance Csig. As a poorly grounded objecttouches or hovers over the panel at multiple locations, the object cancause a negative pixel effect in the panel, which can be observed in thecross-coupling capacitances Cdd and the change in mutual capacitanceCsig. Concurrently, the sense signals can be captured, representative ofthe change in Csig and the negative pixel effect, and the cross-couplingsignals can also be captured, representative of the negative pixeleffect (610).

The touch panel can be switched to the second drive-sense configuration,in which the sense lines can act as drive lines to drive the panel andcapacitively cross-couple, while the drive lines act as sense lines totransmit the sense signals for processing (620). A second scan of thetouch panel can be performed (630). During this scan, multiplestimulation signals can drive the panel along sense lines of the panel.The sense lines can capacitively cross-couple with each other to producecross-coupling capacitances Css. The sense and drive lines cancapacitively couple to produce mutual capacitance Csig. While the poorlygrounded object continues to touch or hover over the panel at multiplelocations, the negative pixel effect can be observed in thecross-coupling capacitances Css and the change in mutual capacitanceCsig. Concurrently, the sense signals on the drive lines can becaptured, representative of the change in Csig and the negative pixeleffect, and the cross-coupling signals at the sense lines can becaptured, representative of the negative pixel effect (635). Bothcaptured sets of sense and cross-coupling signals can be processed(645). In some embodiments, the first set of sense signals can beprocessed using decode matrix M′ to obtain the pixel capacitancesindicative of the touch or hover at the touch panel. The second set ofsense signals can be similarly processed using either decode matrix M′or M′″. Similarly, the first set of cross-coupling signals can beprocessed using cross-coupling matrix N to obtain cross-couplingcapacitances indicative of the negative pixel effect. The second set ofcross-coupling signals can be processed using cross-coupling matrix N orN′.

Both sets of processed cross-coupling signals and processed sensesignals can be used to compensate the sense signals for the negativepixel effect (650). In some embodiments, the corresponding pairs ofcross-coupling signals can be averaged (or otherwise combined) and thecorresponding pairs of sense signals can be averaged (or otherwisecombined) and the cross-coupling average signal can be applied to thecorresponding sense signal average to compensate for negative pixeleffect. In alternate embodiments, the cross-coupling signals in thefirst drive-sense line configuration can be applied to the correspondingsense signals to get a first set of compensated sense signals and,similarly, the cross-coupling signals in the second drive-sense lineconfiguration can be applied to the corresponding sense signals to get asecond set of compensated sense signals. The sets of compensated sensesignals can then be averaged (or otherwise combined). Applying thecross-coupling signal to the sense signal can involve subtracting thecross-coupling signal from the sense signal.

FIG. 7 illustrates an exemplary method for performing a concurrent touchand negative pixel scan and for rejecting noise at a touch panelaccording to various embodiments. The method of FIG.7 can be the same asthe method of FIG. 5, except for the addition of noise rejection. In theexample of FIG. 7, a scan can be performed (705). During the scan, thedrive lines can capacitively cross-couple to produce cross-couplingcapacitances Cdd and the drive and sense lines can capacitive couple toproduce mutual capacitances Csig, as described previously. Additionally,circuitry adjacent to the touch panel, e.g., LCD Vcom circuitry, cancapacitively couple with the touch panel to produce couplingcapacitances Cp, thereby inducing noise in the touch panel.Concurrently, the sense signals can be captured, representative of thechange in Csig and the negative pixel effect, and the cross-couplingsignals, which can include the noise signals, can be captured,representative of the negative pixel effect and the introduced noise(710). The noise can be rejected from the cross-coupling signals and thesense signals (720). The sense signals and the cross-coupling signalscan be further processed (725). The processed cross-coupling signals canbe applied to the processed sense signals to compensate the sensesignals for the negative pixel effect (730). In some embodiments, thecross-coupling signals can be subtracted from the sense signals toperform the compensation.

It is to be understood that concurrent scanning is not limited to themethods of FIGS. 5-7, but can include additional and/or other actionsaccording to various embodiments.

FIG. 8 illustrates an exemplary computing system 800 that can perform aconcurrent touch and negative pixel scan at the system touch panelaccording to various embodiments described herein. In the example ofFIG. 8, computing system 800 can include touch controller 806. The touchcontroller 806 can be a single application specific integrated circuit(ASIC) that can include one or more processor subsystems 802, which caninclude one or more main processors, such as ARM968 processors or otherprocessors with similar functionality and capabilities. However, inother embodiments, the processor functionality can be implementedinstead by dedicated logic, such as a state machine. The processorsubsystems 802 can also include peripherals (not shown) such as randomaccess memory (RAM) or other types of memory or storage, watchdog timersand the like.

The touch controller 806 can also include receive section 807 forreceiving signals, such as touch signals 803 of one or more touch sensechannels (not shown) and other signals from other sensors such as sensor811, etc. The touch controller 806 can also include demodulation section809 such as a multistage vector demodulation engine, panel scan logic810, and transmit section 814 for transmitting stimulation signals 816to touch sensor panel 824 to drive the panel and to force sensor bridge836 to drive the bridge. The panel scan logic 810 can access RAM 812,autonomously read data from the sense channels, and provide control forthe sense channels. In addition, the panel scan logic 810 can controlthe transmit section 814 to generate the stimulation signals 816 atvarious frequencies and phases that can be selectively applied to rowsof the touch sensor panel 824.

The touch controller 806 can also include charge pump 815, which can beused to generate the supply voltage for the transmit section 814. Thestimulation signals 816 can have amplitudes higher than the maximumvoltage by cascading two charge store devices, e.g., capacitors,together to form the charge pump 815. Therefore, the stimulus voltagecan be higher (e.g., 6V) than the voltage level a single capacitor canhandle (e.g., 3.6 V). Although FIG. 8 shows the charge pump 815 separatefrom the transmit section 814, the charge pump can be part of thetransmit section.

Computing system 800 can also include touch sensor panel 824, which canbe as described above in FIG. 1, and display device 830.

Computing system 800 can include host processor 828 for receivingoutputs from the processor subsystems 802 and performing actions basedon the outputs that can include, but are not limited to, moving anobject such as a cursor or pointer, scrolling or panning, adjustingcontrol settings, opening a file or document, viewing a menu, making aselection, executing instructions, operating a peripheral device coupledto the host device, answering a telephone call, placing a telephonecall, terminating a telephone call, changing the volume or audiosettings, storing information related to telephone communications suchas addresses, frequently dialed numbers, received calls, missed calls,logging onto a computer or a computer network, permitting authorizedindividuals access to restricted areas of the computer or computernetwork, loading a user profile associated with a user's preferredarrangement of the computer desktop, permitting access to web content,launching a particular program, encrypting or decoding a message, and/orthe like. The host processor 828 can also perform additional functionsthat may not be related to panel processing, and can be coupled toprogram storage 832 and display device 830 for providing a UI to a userof the device. In some embodiments, the host processor 828 can be aseparate component from the touch controller 806, as shown. In otherembodiments, the host processor 828 can be included as part of the touchcontroller 806. In still other embodiments, the functions of the hostprocessor 828 can be performed by the processor subsystem 802 and/ordistributed among other components of the touch controller 806. Thedisplay device 830 together with the touch sensor panel 824, whenlocated partially or entirely under the touch sensor panel or whenintegrated with the touch sensor panel, can form a touch sensitivedisplay.

Note that one or more of the functions described above, can beperformed, for example, by firmware stored in memory (e.g., one of theperipherals) and executed by the processor subsystem 802, or stored inthe program storage 832 and executed by the host processor 828. Thefirmware can also be stored and/or transported within any non-transitorycomputer readable storage medium for use by or in connection with aninstruction execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch the instructions from the instruction execution system,apparatus, or device and execute the instructions. In the context ofthis document, a “non-transitory computer readable storage medium” canbe any non-transitory medium that can contain or store the program foruse by or in connection with the instruction execution system,apparatus, or device. The computer readable storage medium can include,but is not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus or device,a portable computer diskette (magnetic), a random access memory (RAM)(magnetic), a read-only memory (ROM) (magnetic), an erasableprogrammable read-only memory (EPROM) (magnetic), a portable opticaldisc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory suchas compact flash cards, secured digital cards, USB memory devices,memory sticks, and the like.

The firmware can also be propagated within any transport medium for useby or in connection with an instruction execution system, apparatus, ordevice, such as a computer-based system, processor-containing system, orother system that can fetch the instructions from the instructionexecution system, apparatus, or device and execute the instructions. Inthe context of this document, a “transport medium” can be any mediumthat can communicate, propagate or transport the program for use by orin connection with the instruction execution system, apparatus, ordevice. The transport medium can include, but is not limited to, anelectronic, magnetic, optical, electromagnetic or infrared wired orwireless propagation medium.

It is to be understood that the computing system is not limited to thecomponents and configuration of FIG. 8, but can include other and/oradditional components in various configurations capable of a concurrenttouch panel scan according to various embodiments.

FIG. 9 illustrates an exemplary mobile telephone 900 that can includetouch panel 924, display device 936, and other computing system blocks,and can perform a concurrent touch and negative pixel scan on the touchpanel, according to various embodiments.

FIG. 10 illustrates an exemplary digital media player 1000 that caninclude touch panel 1024, display device 1036, and other computingsystem blocks, and can perform a concurrent touch and negative pixelscan on the touch panel, according to various embodiments.

FIG. 11 illustrates an exemplary personal computer 1100 that can includetouch pad 1124, display 1136, and other computing system blocks, and canperform a concurrent touch and negative pixel scan on the touch panel,according to various embodiments.

The mobile telephone, media player, and personal computer of FIGS. 9through 11 can provide power and processing time savings and improvedtouch and hover sensing, especially for multiple simultaneous touch orhover events, by performing a concurrent touch and negative pixel scanat the touch panel so as to compensate for negative pixel effectaccording to various embodiments.

Although embodiments have been fully described with reference to theaccompanying drawings, it is to be noted that various changes andmodifications will become apparent to those skilled in the art. Suchchanges and modifications are to be understood as being included withinthe scope of the various embodiments as defined by the appended claims.

What is claimed is:
 1. A method comprising: performing a scan at a touchpanel, the scan sensing an object proximate to the touch panel andsensing a negative pixel effect at the touch panel at substantially thesame time; and capturing concurrently: one or more first signalsindicative of the proximity of the object to the touch panel at a firstsensing circuit; and one or more second signals indicative of amagnitude of the negative pixel effect on the touch panel at a secondsensing circuit.
 2. The method of claim 1, comprising: driving a firstset of conductive lines of the touch panel with stimulation signals,wherein the first signals are formed by a capacitive coupling betweenrespective conductive lines in the first set of conductive lines andrespective conductive lines in a second set of conductive lines, andgenerating the second signals on the first set of conductive lines inresponse to the stimulation signals, the second signals formed by acapacitive coupling between one or more pairs of lines of the first setof conductive lines.
 3. The method of claim 1, wherein concurrentlycapturing the first signals and the second signals comprises: capturingthe second signals on a first set of conductive lines of the touchpanel; and capturing the first signals on a second set of conductivelines of the touch panel.
 4. The method of claim 1, comprising:compensating the first signals for the negative pixel effect, thecompensating including applying the second signals to the first signals.5. The method of claim 1, comprising: capturing one or more noisesignals indicative of noise introduced into the touch panel by adjacentcircuitry; and rejecting noise from the touch panel by subtracting thenoise signals from the second signals and the first signals.
 6. Themethod of claim 1, comprising: processing the first signals to determinea capacitance indicative of the proximity of the object, the processingincluding, for m captured first signals, applying a matrix to thecaptured first signals to produce m capacitance values, wherein m is aninteger.
 7. The method of claim 1, comprising: processing the secondsignals to determine a capacitance indicative of the negative pixeleffect on the touch panel, the processing including, for n capturedsecond signals, applying a matrix to the captured second signals toproduce n capacitance values, wherein n is an integer.
 8. The method ofclaim 1, further comprising performing a second scan at the touch panelduring a same scan period as the scan at the touch panel.
 9. A touchsensitive device comprising: a touch panel including drive lines andsense lines, the drive lines configured to drive the touch panel tosense a proximate object and to generate second signals indicative of agrounding condition of the object and the sense lines configured togenerate first signals indicative of a proximity of the object; andtouch circuitry including: a first circuit configured to capture thefirst signals based on capacitive coupling between pairs of the driveand sense lines, and a second circuit configured to capture the secondsignals based on capacitive coupling between pairs of the drive lines,wherein the first signals and the second signals are capturedconcurrently.
 10. The device of claim 9, wherein the first circuit ofthe touch circuitry comprises: a drive circuit configured to supply adriving voltage to the drive lines to drive the touch panel; and a sensecircuit configured to capture the first signals and to process thecaptured first signals.
 11. The device of claim 9, wherein the secondcircuit of the touch circuitry comprises: a coupling circuit configuredto capture the second signals, to isolate the captured second signals,and to process the isolated second signals.
 12. The device of claim 9,wherein the touch circuitry comprises: a switching circuit configured toswitch between multiple configurations of the drive and sense lines. 13.The device of claim 9, wherein the touch circuitry comprises: a noiserejection circuit configured to reject noise introduced into the touchpanel by adjacent circuitry.
 14. The device of claim 9 incorporated intoat least one of a mobile telephone, a digital media player, or aportable computer.
 15. A non-transitory computer readable storage mediumstoring instructions to perform a method of a computing device includinga touch sensing surface, the method comprising: performing a scan at atouch panel, the scan sensing an object proximate to the touch panel andsensing a negative pixel effect at the touch panel at substantially thesame time; and capturing concurrently: one or more first signalsindicative of the proximity of the object to the touch panel at a firstsensing circuit; and one or more second signals indicative of amagnitude of the negative pixel effect on the touch panel at a secondsensing circuit.
 16. The non-transitory computer readable storage mediumof claim 15, the method further comprising: driving a first set ofconductive lines of the touch panel with stimulation signals, whereinthe first signals are formed by a capacitive coupling between respectiveconductive lines in the first set of conductive lines and respectiveconductive lines in a second set of conductive lines, and generating thesecond signals on the first set of conductive lines in response to thestimulation signals, the second signals formed by a capacitive couplingbetween one or more pairs of lines of the first set of conductive lines.17. The non-transitory computer readable storage medium of claim 15, themethod further comprising: capturing the second signals on a first setof conductive lines of the touch panel; and capturing the first signalson a second set of conductive lines of the touch panel.
 18. Thenon-transitory computer readable storage medium of claim 15, the methodfurther comprising: compensating the first signals for the negativepixel effect, the compensating including applying the second signals tothe first signals.
 19. The non-transitory computer readable storagemedium of claim 15, the method further comprising: capturing noisesignals indicative of noise introduced into the touch panel by adjacentcircuitry; and rejecting noise from the touch panel by subtracting thenoise signals from the second signals and the first signals.
 20. Thenon-transitory computer readable storage medium of claim 15, the methodfurther comprising: processing the first signals to determine acapacitance indicative of the proximity of the object, the processingincluding, for m captured first signals, applying a matrix to thecaptured first signals to produce m capacitance values, wherein m is aninteger.
 21. The non-transitory computer readable storage medium ofclaim 15, the method further comprising: processing the second signalsto determine a capacitance indicative of the negative pixel effect onthe touch panel, the processing including, for n captured secondsignals, applying a matrix to the captured second signals to produce ncapacitance values, wherein n is an integer.
 22. The non-transitorycomputer readable storage medium of claim 15, the method furthercomprising performing a second-scan at the touch panel during a samescan period as the scan.